She said: “I also know that many other people believe strongly that in the whole of the article, what Mr Johnson appears to have been attempting to do was to say that there shouldn’t be a ban and that he was engaging in a legitimate debate.”

Asked what she made of the language used by the ex-cabinet minister, Ms Dick told the BBC Asian Network: “Some people have clearly found it offensive.

“I spoke last night to my very experienced officers who deal with hate crime and, although we have not yet received any allegation of such a crime, I can tell you that my preliminary view having spoken to them is that what Mr Johnson said would not reach the bar for a criminal offence. He did not commit a criminal offence.”

Pressed further on Mr Johnson’s choice of language given recent spikes in hate crime, the Commissioner said: “I think everybody in public life has to think about the impact of what they say.

“I also think that I am proud to police in a liberal democracy in which people have the right to express their opinions.

“What Mr Johnson said, if it is not criminal, is a matter for Mr Johnson and his friends and colleagues and indeed for the Conservative Party.”

The police and Crown Prosecution Service define a hate crime as “any criminal offence which is perceived by the victim or any other person, to be motivated by hostility or prejudice, based on a person’s disability or perceived disability; race or perceived race; or religion or perceived religion; or sexual orientation or perceived sexual orientation or transgender identity or perceived transgender identity”.

Cressida Dick said officers assess that Mr Johnson did not commit an offence (Victoria Jones/PA)

If an alleged crime is reported, police investigate whether it amounts to a hate offence. If a case is referred to the CPS, prosecutors would need enough evidence to convince the court that the crime was motivated by or demonstrated hostility.

Mr Johnson has been urged by a number of senior Tories to apologise.

But sources close to him have made clear that he stood by the article, in which he argued against a burka ban of the kind adopted by some European countries.

Supporters have also suggested that the Brexiteer is being targeted in an attempt to ward off a possible challenge to Mrs May in the autumn, when negotiations with the EU will come to a head.

The row moved into its fourth day on Thursday, with pressure mounting on the Conservative Party leadership to decide whether to take action against Mr Johnson, who was maintaining his silence on a holiday break.

The founder of the Conservative Muslim Forum, Lord Sheikh, has written to party chairman Brandon Lewis demanding “serious action”, while former attorney general Dominic Grieve said he would quit the partyif Mr Johnson became leader.

Disciplinary action could lead to Mr Johnson being suspended or even expelled if he was found to be in breach of the Tory code of conduct, but would risk igniting civil war in a party many of whose members see him as the best option to succeed Mrs May as leader.

Critics have accused Mr Johnson of using the row to win right-wing support in any future leadership battle.

A Sky News poll found that 45% of voters thought he should apologise, while 48% thought he should not.